The present invention relates to a method of preparing polyurethane packaging foam for dispensing into a container in which an article is present to be packaged for shipping, wherein the temperature of the polyurethane foam being dispensed into the container is lower, as is the maximum reaction exotherm temperature.
Foam-in-place polyurethane packaging foam provides a custom made barrier of defense for products against shock, vibration, and impact and protects such products during shipment. Products are placed in a carton into which liquid foam is dispensed, usually from a foam dispensing gun commonly used in the industry. Isocyanate and polyol precursors are separately introduced into a mixing chamber within the gun. The reaction takes place instantaneously and the reaction product is promptly dispensed into the container and continues reacting and expanding about the article in the container which is being packaged. The container is usually closed while the reaction continues so as to substantially completely fill the spaces about the article with polyurethane foam. The foam cures, expanding up to 200 times its liquid volume and filling the space around the product.
Generally, polyurethane foam precursors are shipped in separate containers of specially blended "A" and "B" liquids. The foam-in-place packaging equipment at the customer's location separately conducts the precursors from the containers to the dispensing gun where the two components are mixed in a mixing chamber to form the polyurethane foam. The "A" component is usually the polymeric isocyanate and the "B" component principally contains polyoxyalkylated polyol and water.
Water reacts with a portion of the polymeric isocyanate to form carbon dioxide, which serves as a blowing agent for the foam. Heat is both a reactant and a product of this reaction. Heat is used to initiate the reaction and the precursors are heated as they travel through heated chemical conduits from their respective containers to the dispensing gun. Additionally, heat is exothermically generated from the reaction of the isocyanate and the polyol and serves to cure the foam quickly. Such heat is referred to as an exotherm.
Prior to the Montreal Protocol mandate, trichloromonofluoromethane (CFC-11) was used as an auxiliary blowing agent. CFC-11 containing systems not only required less initial heat, but also produced a lower exotherm. However, the use of fluorocarbons is being discouraged because of the adverse effect they have on the atmosphere and, in particular, the ozone layer at the higher altitudes.
The extra heat required to blow with carbon dioxide strains the heated chemical conduits. The heat produced from the reaction of an isocyanate, polyol and water, wherein carbon dioxide is formed as the blowing agent, is higher than when CFC-11 blowing is present and would potentially adversely affect the product being packaged The present invention resulted from a need to reduce the liquid dispensing temperatures of the reaction product as well as the maximum reaction exotherms in carbon dioxide blown polyurethane packaging foams. Most electronic components packaged in foam-in-place polyurethane packaging foam are sensitive to heat, therefore the less heat evolved, the less potential for damage.
Polyurethane slabstock foam processing utilizes the incorporation of air bubbles into the mixing chamber. A more efficient reaction will occur due to the hypothesis that air bubbles provide nucleating sites for the chemicals to react. The present invention allows nucleating sites to form and produces a similar situation in a two component system wherein the liquid polyurethane foam is being dispensed from a foam dispensing gun of a foam-in-place packaging equipment.